[Post-Install] Logged out screen weirdness.......

[fatbloke]

So, a couple of weekends back, I was doing my 25.10 updates (which completed). Then I was offered the 26.04 LTS upgrade - which I accepted, followed the prompts and left it to do it's thing.

Now, when I log off/out, I get back to the login screen/page ok, but my monitor doesn't drop back to standby/hibernate/sleep or whatever it's called. The login boxes do disappear, but the background screen remains. The only way I can manage it is to either hit the sleep or hibernate options, or of course, hit the off button on the monitor itself.

I did a bit of a search, but that said about it being managed by SDDM, which should be in the settings, but it's not. None of the suggested stuff shows up on my system as far as I can work out.

Any guidance is much appreciated........

[Schwarzer Kater]

Did you already try the following things in System Settings?

• check your Screen Locking (section: Security & Privacy) settings
• check your Power Management (section: System) settings
• [Apply Plasma Settings…] (button at the top) in -> Colours & Themes (section Appearance & Style) -> Login Screen (SDDM)

[fatbloke]

Did you already try the following things in System Settings?

• check your Screen Locking (section: Security & Privacy) settings
• check your Power Management (section: System) settings
• [Apply Plasma Settings…] (button at the top) in -> Colours & Themes (section Appearance & Style) -> Login Screen (SDDM)

Thank you for the kind response. Checked the items you suggested and to see if anything happens I've changed a few of the options. So now about to log out and see if it has reverted to how it used to work before the upgrade.

[fatbloke]

Doesn't seem to have made any difference. The only way I seem to have to blank the screen i.e. put it into standby, is to actually hit the power button on the monitor.

I know I've been meddling with linux for a long time, but I still know little to nothing about the guts of how it works. Hence, I still have no idea about where to look and what for, so any suggestion is still very much appreciated.

[die.boer]

please post output of

inxi -Sxxx

systemctl status sddm --no-pager

grep -R "DisplayServer" /etc/sddm.conf*​

[fatbloke]

please post output of

inxi -Sxxx

systemctl status sddm --no-pager

grep -R "DisplayServer" /etc/sddm.conf*​

it's saying
"inxi -Sxxx
System:
Host: johnsPC Kernel: 7.0.0-27-generic arch: x86_64 bits: 64 compiler: gcc
v: 15.2.0 clocksource: tsc
Desktop: KDE Plasma v: 6.6.4 tk: Qt v: N/A wm: kwin_wayland vt: 2 dm: SDDM
Distro: Kubuntu 26.04 LTS (Resolute Raccoon) base: Ubuntu"

then I get this
"systemctl status sddm --no-pager
● sddm.service - Simple Desktop Display Manager
Loaded: loaded (/usr/lib/systemd/system/sddm.service; enabled; preset: enabled)
Active: active (running) since Sat 2026-06-27 08:17:20 BST; 4min 51s ago
Invocation: 7ae305630db847439b08a57e672f94f2
Docs: man:sddm(1)
man:sddm.conf(5)
Process: 6605 ExecStartPre=/bin/sh -c [ "$(cat /etc/X11/default-display-manager 2>/dev/null)" = "/usr/bin/
sddm" ] (code=exited, status=0/SUCCESS)
Main PID: 6619 (sddm)
Tasks: 2 (limit: 8668)
Memory: 22.7M (peak: 27.6M)
CPU: 78ms
CGroup: /system.slice/sddm.service
└─6619 /usr/bin/sddm

Jun 27 08:17:29 johnsPC sddm[6619]: Authentication for user "john" successful
Jun 27 08:17:29 johnsPC sddm-helper[9778]: pam_kwallet5(sddm:setcred): pam_kwallet5: pam_sm_setcred
Jun 27 08:17:29 johnsPC sddm-helper[9778]: pam_unix(sddm:session): session opened for user john(uid=10…(uid=0)
Jun 27 08:17:29 johnsPC sddm[6619]: Auth: sddm-helper exited successfully
Jun 27 08:17:29 johnsPC sddm[6619]: Greeter stopped. SDDM::Auth::HELPER_SUCCESS
Jun 27 08:17:29 johnsPC sddm-helper[9778]: gkr-pam: unlocked login keyring
Jun 27 08:17:29 johnsPC sddm-helper[9778]: pam_kwallet5(sddm:session): pam_kwallet5: pam_sm_open_session
Jun 27 08:17:29 johnsPC sddm-helper[9778]: Starting Wayland user session: "/etc/sddm/wayland-session" …ayland"
Jun 27 08:17:29 johnsPC sddm[6619]: Session started true
Jun 27 08:17:29 johnsPC sddm-helper[9778]: Failed to write utmpx: No such file or directory
Hint: Some lines were ellipsized, use -l to show in full."

And finally I get this with the third command suggested...
"grep -R "DisplayServer" /etc/sddm.conf*
/etc/sddm.conf.d/10-wayland.conf:DisplayServer=wayland"


All of which, is stuff I've not seen before. Been so long since I had to try and learn how to fix anything, I can't even follow what it's trying to tell me.......

[die.boer]

and output of

lspci | grep -Ei "vga|3d|display"

please

[die.boer]

quick test you can do , run

sudo nano /etc/sddm.conf.d/10-wayland.conf

look for
[General]
DisplayServer=wayland and change it to
[General]
DisplayServer=x11
save and exit ( ctrl+O - enter - ctrl+X )
reboot
If it works properly then it confirmed it's specifically the Wayland greeter that's failing to trigger DPMS.
If it makes no difference, simply change it back to wayland.